Nitzschia transtagensis Morales, Novais, Wetzel, Morais & Ector (Bacillariophyceae) – the second record in the Mediterranean Region

Abstract

The Mediterranean Region holds significant ecological importance, characterised by its unique climate, biodiversity and the crucial role it plays in global ecosystems. Mediterranean streams are naturally highly-stressed environments mainly due to fluctuations in water quantity. River flow generally varies from perennial to ephemeral and temporary rivers constitute significant water resources. Streams that flow through Balearic Islands are subjected to these conditions. The majority of these streams sustain water flow for 4–5 months annually, with exceptions noted for streams associated with springs, which typically maintain water throughout most of the year.Benthic diatoms are widely recognised as reliable bioindicators of water quality, used in many aquatic ecosystems. Analysing diatom communities and their biodiversity serves as a valuable tool to ensure the ecological and sustainable utilisation of water resources as well as the accurate development of guidelines for their conservation.The field of diatom taxonomy and distribution plays a crucial role in advancing our understanding of aquatic ecosystems and their biodiversity. Species of the genus Nitzschia are extensively found throughout the Mediterranean Region, including the Balearic Islands. However, they have rarely been investigated in temporary streams.This study presents the first record of Nitzschia transtagensis Morales, Novais, Wetzel, Morais & Ector, outside the type locality and being the second record in Europe. In this study, the authors found this taxon in one temporary stream of Majorca Island, Torrent des Castellot in November 2005 (Balearic Islands). Nitzschia transtagensis occurred at 2.6% abundance in this stream with oligotrophic waters (0.052 mg∙l-1 of nitrate), slightly alkaline pH values (7.8) and water conductivity levels of 626.5 µS cm-1. This species was recorded in the biofilm of the stones together with other taxa such as Achnanthidium minutissimum (Kützing) Czarnecki (39.2%), Gomphonema rosenstockianum Lange-Bertalot & Reichardt (28.9%) and Halamphora oligotraphenta (Lange-Bertalot) Levkov (20.4%). The Nitzschia transtagensis frustules found in the examined material have similar dimensions and a higher fibulae count (8–11 in 10 μm vs. 6–10 in 10 μm) compared to the type material of Nitzschia transtagensis. The habitat characteristics in which this species was found are described, together with LM micrographs of this taxon.

Keywords

• diatom
• distribution
• ecology
• epilithon
• taxonomy